Precision cutting of multiple parts from larger workpieces or stock members typically is accomplished by gripping the larger workpiece in a vise assembly and cutting the same with a cutting device, such as a band saw, at a position very close to the vise. The workpiece then advanced beyond the vise and another cut is made. When production runs are undertaken, in which many parts are to be cut from elongated bar or tube stock, the workpieces are automatically advanced for each new cut by a shuttle vise assembly positioned next to the vise at the cutting tool.
Virtually all bar stock, and particularly high-strength, tubular, metal stock, will have internal stress in the stock itself, which stress will be relieved partially when the stock is cut. Moreover, the end of the workpiece being cut off often is supported on the other side of the cut by a workpiece rest or stop and, in some cases, by a vise. As the bar is being cut, therefore, the workpiece will be supported on both ends, much as a beam is supported. When the cut is complete, however, the cut end and the workpiece each become cantilever supported, one from the saw fixed vise and the cut part from the rest or vise on the other side of the cut.
Upon the completion of a cut, therefore, internal stress in the stock and cut part are relieved and both have their support changed from a beam to a cantilever with the end at the cut line free to move. Such movement predictably does occur.
This problem is made worse when tubular stock is cut because the residual internal stress in the tube from the tube forming process is greater. Moreover, when bar stock is bundled and multiple side-by-side pieces cut, the potential for movement is still greater.
FIG. 1 illustrates the above-described precision cutting problem in connection with production cutting of a bundle of workpieces with a band saw. Band saw apparatus 10a, whether designed primarily for vertical or horizontal cutting, includes a saw head assembly (not shown), which movably supports a flexible continuous loop saw blade 11a. A cutting table 12a upon which workpieces 13a are placed may be provided as part of saw assembly 10a, or as a separate workpiece feed table. Band saw blade 11a is movably mounted around a pair of wheels (not shown), one of which is driven. Two or more blade guide assemblies (not shown) are mounted to the head assembly between the wheels and slidably engage saw blade 11a to orient it in a cutting orientation. A "cutting stretch" is defined intermediate the saw blade guide assemblies where advancing saw blade 11a cuts workpieces 13a. During motion or advancement of the blade, one of band saw blade 11a and workpieces 13a are displaced relative to the other along a guided path known as the "cutting line" 14a, the center line of the desired line of cut. The actual groove, gap or channel of material removed by saw blade 11a during cutting is the "kerf" 15a (FIG. 3).
Typically, as shown in FIG. 1, a plurality of elongated workpieces 13a are positioned in a side-by-side relation and are collectively gripped to form bundle 16a by a fixed vise mechanisms 17a on one side of blade 11a and a second vise 20a, or by a workpiece rest or support (FIGS. 4A-4D) mounted to table 12a on the opposite side of cutting line 14a. Further, a shuttle vise assembly 21a also grips the bundle of workpieces 13a at an area away from the cutting line and periodically advances bundle 16a forward toward cutting line 14a. Shuttle vise assembly 21a is movably mounted on a track or guide way or rail assembly 23a on a feed table, and the shuttle vise 21a reciprocates toward and away from cutting line 14a. Each vise mechanism 17a, 20a and 21a includes a pair of spaced-apart gripping jaws 24a, 24a'; 25a, 25a'; and 26a, 26 a', respectively, positioned on opposite sides of bundle side portions 27a and 27a'. The corresponding jaws of each vise mechanism 17a, 20a and 22a engage side portions 27a and 27a' of the workpieces, and at least one of the jaws is movable toward the other to allow gripping of bundle 16a.
Band saw apparatus 10a typically includes a movable head assembly so arranged as to be moved toward and away from the workpieces by suitable means, such as a hydraulic motor or pneumatic apparatus. Thus, in cutting operations, the saw head assembly is displaced, which moves the cutting stretch and hence saw blade 11a, along cutting line 14a relative to table 12a and fixed vises 17a and 20a. This enables the driven band saw blade 11a to cut across bundle 16a, which is securely held between the respective jaws of fixed vises Further, shuttle vise assembly 21a periodically advances bundle 16a forward after the completion of each cutting cycle so that the workpieces can be cut again. A typical band saw apparatus employing a fixed vise and a shuttle vise assembly is disclosed in more detail in U.S. Pat. No. 4,179,961 to Harris, which is incorporated herein by reference.
Typically the band saw head assembly moves saw blade 11a across bundle 16a from a staring position 28a (blade 11a shown in solid lines in FIG. 1) to a finishing position 30a (blade 11a shown in broken lines in FIG. 1) where the cutting edge 31a of blade 11a has cut completely through bundle 16a to sever cut portions or parts 32a from workpieces 13a. As shown in FIGS. 1 and 3, the blade in finishing position 30a is positioned so that cutting edge 31a is just past side portion 27a of bundle 16a. Since cut portions 32a have been completely severed, it is generally regarded as time consuming and wasteful in production band saw cutting to advance blade 11a any further along cutting line 14a. Thus, the controller (not shown) controlling movement of the band saw head assembly will stop advancing the cutting head once cutting edge 31a passes through the last workpiece. Often this is set by a movable stop or limit switch (not shown) which terminates advancement of the cutting head.
Once saw blade 11a has moved to finishing position 30a and before cut portions 32a have been removed from vise mechanism 20a, the saw assembly is returned back along kerf 15a and cutting line 14a starting position 28a. This immediate return of the cutting blade minimizes cycle time, which directly affects the cost of cutting of each part.
As above indicated, one common problem encountered when cutting workpieces, and particularly multiple elongated workpieces 13a, is that after saw blade 11a has severed cut portions 32a from bundle 16a, kerf 15a intermediate bundle 16a and cut parts 32a tends to move or close as the internal and clamping stresses are relieved by the cut. This is particularly true for rectangular parallelpiped tubular members, as shown in FIGS. 1-3, and for shorter cut parts 32a, as illustrated in FIG. 4A. With regard to the rectangular, tubular workpieces of FIGS. 1-3, the internal stress of tube formation is relieved during cutting which causes opposite side walls 35a and 35a' proximate individual workpiece ends 34a to flare outwardly (shown exaggerated in broken lines in FIG. 2). In turn, this flaring causes adjacently disposed end portions 33a and 34a of cut portions 31a and workpieces 13a, respectively, to fan outwardly creating the arc-shaped cut ends 33a and 34a, as viewed in FIGS. 1 and 3.
Upon closer inspection, FIG. 3 illustrates that bunching of the flared cut portion ends 33a causes portions thereof to protrude into kerf 15a, which closes the kerf between workpiece ends 34a and cut portion ends 33a.
Hence, upon return of saw blade 11a along cutting line 14a, blade cutting edge 31a often contacts the moved respective ends of cut portions 32a and/or workpieces 13a. Over the course of use, such contact accelerates wear of the saw blade cutting edge 31a (most typically the side facing cut portions 32a). Moreover, in some cases the movement on relief of the internal and clamping stresses is enough that kerf 15a closes sufficiently to wedge against or hook the blade and pull it off of the drive and idler wheels, with disastrous results. Often the blade will be broken, and at a minimum the production process must be shut down and the blade remounted to the cutting head assembly.
Even if the blade is only pulled across the parts, one side of cutting edge 31a will become dull. This results in imprecisely cut workpiece ends 34a and cut portion ends 33a. These deviations not only adversely affect precision and accuracy, but in extreme situations, may necessitate scrapping of cut portions 32a altogether.
When relatively short parts 32a are cut, movement also is quite likely. The shorter length often precludes proper gripping between jaws 25a and 25a' of fixed vise mechanism 20a, and shorter cut portions 32a may not even be gripped during severing. As saw blade 11a cuts through bundle 16a, cut portions 32a are sometimes randomly misaligned, which causes end 33a of cut portions 32a to protrude into kerf 15a. Similarly, during retraction of saw blade 11a back to starting position 28a, cut portion ends 33a interfere or impede movement of blade 11a through kerf space 15a. This causes one side of the cutting edge 31a of the saw blade to dull prematurely or the blade to be in danger of being pulled off the blade support wheels.